1. Field of the Invention
The present invention relates to a method for producing an L-amino acid using a microorganism. L-amino acids are used in a variety of fields including, for example, seasonings, food additives, feed additives, chemical products, and pharmaceutical products.
2. Brief Description of the Related Art
L-amino acids, such as L-threonine and L-lysine, have been industrially produced by fermentation using L-amino acid-producing bacteria such as bacteria belonging to the genus of Escherichia. Examples of such L-amino acid-producing bacteria include bacterial strains isolated from nature, artificial mutant strains thereof, and genetic recombinant strains having enhanced activity of L-amino acid biosynthetic enzyme. Examples of a method for producing L-threonine include the methods described in Japanese Laid-Open Patent Application No. 5-304969, WO98/04715, Japanese Laid-Open Patent Application No. 5-227977, and US2002-0110876. Examples of a method for producing L-lysine include the methods described in Japanese Laid-Open Patent Application No. 10-165180, Japanese Laid-Open Patent Application No. 11-192088, Japanese Laid-Open Patent Application No. 2000-253879, and Japanese Laid-Open Patent Application No. 2004-129666. Examples of carbon sources used in the fermentation production of L-amino acids include saccharides, such as, glucose, fructose, sucrose, blackstrap molasses, and starch hydrolysates.
Clark, D. P. and Cronan (J. E. Jr. 1996. p. 343-357. In F. D. Neidhardt (ed.), Escherichia coli and Salmonella Cellular and Molecular Biology/Second Edition, American Society for Microbiology Press, Washington, D.C.) explain that wild type Escherichia coli is able to grow using a long-chain fatty acid having a carbon chain with 12 or more carbon atoms as the sole carbon source. Weeks, G. et al. (1969. Control of Fatty Acid Metabolism I. Induction of the Enzymes of Fatty Acid Oxidation in Escherichia coli. J. Bacteriol. 97: 827-836) explain that wild type Escherichia coli is able to grow in a medium using myristic acid, palmitic acid or oleic acid as a sole carbon source. Additionally, Clark, D. P. and Cronan, J. E. Jr. (1996. p. 343-357. In F. D. Neidhardt (ed.), Escherichia coli and Salmonella Cellular and Molecular Biology/Second Edition, American Society for Microbiology Press, Washington, D.C.) and Campbell J. W. et al. (2003. A new Escherichia coli metabolic competency: growth on fatty acids by a novel anaerobic beta-oxidation pathway. Mol. Microbiol. 47: 793-805) describe that fatty acids are utilized by enzymes encoded by a group of genes including fadL, fadD, fadE, fadB, fadA, fadJ and fadI, via a pathway called beta oxidation, and that such a group of fad genes is subject to repression by a transcription factor encoded by fadR. Furthermore, as shown in Cronan, J. E. Jr. and Subrahmanyam, S. (1998. FadR, transcriptional co-ordination of metabolic expediency. Mol. Microbiol. 29: 937-943), there are some reports about a strain lacking the fadR gene. However, as shown in Vorum, H. et al. (1992. Solubility of long-chain fatty acids in phosphate buffer at pH 7.4. Biochimica et Biophysica Acta, Lipids and Lipid Metabolism 1126: 135-142), the solubility of a fatty acid is, in general, extremely low and so far, there are no examples of production of a substance by a direct fermentation method using a fatty acid as the major carbon source. Thus, in order to use the fatty acid as the carbon source for production of L-amino acids, it is very important that the fatty acid in a medium is physiologically treated so that it is more usable and so that fatty acid utilization by a fermentative bacterium is enhanced. Thus far, there have been no reports that explain the effects of deletion or amplification of genes involved in fatty acid utilization or substance production using fatty acids as carbon sources.
Japanese Laid-Open Patent Application No. 2004-129666 discloses a method for producing L-threonine using a microorganism lacking the fadR gene on its chromosome. Additionally, Japanese Laid-Open Patent Application No. 2002-017363 discloses a method for producing a substance by enhancing a respiratory chain pathway with high-energy acquiring efficiency or deleting a respiratory chain pathway with low-energy acquiring efficiency. However, in both cases the carbon source was glucose. Neither study described any significant effects in cases where fatty acids were used as carbon sources.